Watch out: It has higher shrinkage (up to 1%) and a shorter "library life," often becoming brittle after 1–2 years. 2. Select the Right Hardness (Shore A)
Hardness is measured on the . Lower numbers are softer and more flexible: Mold Making and Casting Products by Category - Smooth-On
Best for: Food-safe applications (if certified), resin casting, and high-detail prototypes.
Generally considered the "gold standard" for its extreme dimensional accuracy and longevity . It has virtually zero shrinkage (around 0.04%) and can last for decades.
Best for: Beginners, large industrial molds, and masters that might contain sulfur or other contaminants.
Watch out: It is susceptible to —if it touches sulfur (found in some clays), latex, or certain 3D prints, it may stay gooey and never harden.